Conventionally, as described in, for example, Japanese Unexamined Patent Publications No. 09-161814 and 11-329489, a method of manufacturing a battery has been known in which a cathode or a positive electrode and an anode or a negative electrode are laminated while holding a separator between the electrodes for the purpose of preventing a short circuit therebetween to form an electrode/separator laminate, or in which a cathode (or an anode), a separator, an anode (or a cathode) and a separator are laminated in this order, and the laminate is wound up to form an electrode/separator laminate; and then the electrode/separator laminate thus prepared is charged into a battery container, an electrolytic solution is poured into the battery container; and then the container is sealed.
However, in such a method of manufacturing a battery, the electrode and the separator are liable to cause mutual slip movement during storage or transport of the electrode/separator laminate. As a result, the problems are that the productivity of a battery is low and that inferior goods are liable to occur. Further, according to the battery thus obtained, the electrode swells or shrinks during use thereof, so that adhesiveness between the electrode and the separator becomes worse, leading to a reduction in battery characteristics, or an internal short circuit occurs, whereby the battery causes heat generation and temperature rise, occasionally leading to even the possibility of causing melting and breakage of the separator.
Conventionally, various methods of manufacturing a porous film for use as such a separator in manufacturing of a battery have been known. As one of the methods, as described in, for example, Japanese Unexamined Patent Publication No. 09-012756, a method is known in which a sheet is manufactured from a gel composition comprising a ultra-high molecular weight polyolefin resin and a polyolefin resin with a high molecular weight distribution (weight average molecular weight/number average molecular weight) and stretched in a high ratio. However, such a battery separator made of a porous film obtained by stretching in a high ratio still has a notable heat shrinkability under a high temperature environment such as the case where the battery causes an abnormal temperature rise by an internal short circuit and the like, and according to the circumstances, the problem is that the battery separator suffers melting and breakage so that it does not function as a diaphragm between electrodes.
In order to improve the safety of a battery, it is an important issue to both improve the heat resistance and reduce the heat shrinkage factor of the battery separator under such a high temperature environment. As to this issue, in order to control the heat shrinkage of the battery separator under a high temperature environment, as described in, for example, Japanese Unexamined Patent Publication No. 05-310989, a method is also known in which a ultra-high molecular weight polyethylene and a plasticizer are melt-kneaded, the mixture is extruded into a sheet from a die, and the plasticizer is then extracted and removed to provide a porous film for use as a battery separator.
The porous film obtained by this method does not melt or break even under a high temperature environment and is superior in heat resistance; however, contrary to the above-described method, the film has not been subjected to stretching in manufacturing processes, and therefore the strength is not sufficient and the problem of heat shrinkage is not improved. Thus, a porous film for use as a separator which does not melt or break, and has a small heat shrinkage factor under a high temperature environment has not conventionally been known.
The present invention has been completed to solve the problems as described above in the conventional manufacture of a battery. Therefore, it is an object of the invention to provide an adhesive-carrying porous film for use as a battery separator, which, in manufacturing a battery, is useful for efficient manufacture of a battery as it forms an electrode/separator laminate comprising an electrode and a separator temporarily bonded to each other so that there is caused no mutual slip movement between the electrode and the separator and which itself, after manufacturing a battery, functions as a separator which does not melt or break, and has a small heat shrinkage under high temperatures. Furthermore, it is another object of the invention to provide a method of manufacturing a battery by using such an adhesive porous film.